In plastic lidded containers, it is desirable to provide a strong attachment and good seal between the container and the lid, especially for shipping purposes. Usually, interlocking or inter-engaging flanges are provided respectively on the lid and the upper peripheral edge portion of the container to retain the lid on the container. The difficulty is that the stronger the engagement between these interlocking flanges, and thus the stronger the attachment of the lid to the container, the more difficult it is to remove the lid when it is desired to do so. Ideally, one would like to have good engagement between the lid and the container for shipping purposes, and some means for relieving or reducing the force of engagement between the lid and the container when it is desirable to remove the lid
One method of accomplishing the above objectives is to provide the lid with a tear-off strip that contains the lid locking flange that engages the container locking flange. When the lid is on the container, the engaged locking flanges hold the lid securely onto the container. When it is desired to remove the lid, the lid tear-off strip is removed, so there is no longer any locking engagement between the lid and the container.
However, while this method facilitates removal of the lid, it suffers to the extent that it does not provide for a secure fit between the lid and the container after the tear-off strip has been removed. As well, as there is no residual physical connection between the container and lid, the lid may need to be set down on a suitable surface for access to be gained to the contents of the container; this can result in the lid becoming soiled, whereupon the contents of the container can become contaminated, or on the surface becoming soiled with the contents of the container.
One method of overcoming the former difficulty, namely, for providing a secure fit between the lid and container after removal of the tear-off strip is shown in U.S. Pat. No. 4,735,337 issued to John W. Von Holdt. In this patent, the lid outer skirt that contains the lid locking flange is provided with a zigzag tear line that defines a tear-off strip. The tear line passes repeatedly through the lid locking flange, so that upon removal of the tear-off strip, only spaced-apart portions of the lid locking flange remain.
As to the latter difficulty, it will be evident that, in the case of a rectangular lid having two parts separated by an integral hinge (i.e. a linear portion formed of flexible material), if the lid locking flange is retained along a first of said parts, and intermittently along a second of said parts (for example, by the Von Holdt method), the first part will be relatively securely fastened to the container, while the second is relatively easily hingedly removed, to permit access to the contents. However, inter alia, this method suffers in that, in order to provide for secure fastening, the first part must block at least a portion of the container opening.